This is one of Paul's collector fins. Very nicely formed using tools he built.
He used Permatex Copper Spray a Gasket to adhere and thermally bond the aluminum fin to the copper riser pipe. This may give better thermal performance -- something I hope to test fairly soon.

The fins were painted by the moderately selective paint called Thermalox -- this paint is available in easy to apply spray cans and gives a lower emissivity finish that should reduce collector heat loss and improve performance.

This is Paul's collector -- it uses a metal frame made from galvanized steel stud "rail" material.

To store the collected solar heat, Paul uses two barrels, each with a new version of the coil of PEX type of heat exchanger that uses two coils of small diameter PEX pipes in parallel to transfer heat from the solar storage to the potable water. John Canivan's JC-SolarHomes website has quite a bit of material on using drums for solar heat storage.

Paul worked out an innovative way to moving the fairly heavy collector up on to his high roof -- probably not OSHA approved, but it worked: